The invention is directed to a torsional vibration damper with a driving side transmission element.
DE 44 44 196 A1 shows a torsional vibration damper having a driving-side transmission element in the form of a first flywheel mass and a driven-side transmission element in the form of a second flywheel mass which is rotatable relative to the first flywheel mass. The two flywheel masses are connected with one another by a damping device in the form of energy accumulators, wherein a gearset comprising at least one driving-side gearset element in the form of a planet wheel in a working connection with a sun wheel and comprising a driven-side gearset element in the form of a ring gear is associated with the damping device. The torsional vibrations introduced on the drive side can be transmitted to the damping device with a gear ratio or gear shifting by means of the gearset. As can be seen from the Offenlegungsschrift, or laid open application, this results in the advantage of a different adjustment capability of the energy accumulators, so that the driving-side transmission element and the driven-side transmission element have only a small relative rotation relative to one another. This results approximately in the effect of a comparatively large total mass so that the mass moment of inertia which acts counter to fluctuations in the synchronous running of the driving means is apparently increased compared with a torsional vibration damper in which larger relative movements are possible between the individual masses. This results in small variations in torque at the engine front.
Among the positive contributions to these results is the fact that with the introduction of torsional vibrations and the resulting relative movements between the driving-side and the driven-side transmission elements, the gearset elements are accelerated, so that fast relative deflections of the transmission elements due to the high acceleration at the gearset elements have the effect of a large mass moment of inertia. The effect of this large mass moment of inertia is particularly advantageous at low rates of rotation of the driving means, for example, an internal combustion engine, because the natural frequency of the torsional vibration damper in lower speed ranges can be damped by an increasing mass moment of inertia, so that the torsional vibration damper always stays above the critical range at the normal operating speeds of such an internal combustion engine.
With an increasing rate of rotation in the internal combustion engine, however, the introduced torsional vibrations reach higher frequencies at a small magnitude, so that the large mass moment of inertia undesirably manifests itself in that these torsional vibrations are transmitted to the transmission side without satisfactory dampening.
In another torsional vibration damper described in DE 36 30 398 A1, the dampening device must make do without a gearset bringing about a gear ratio change. Because of the lower mass moment of inertia compared with the torsional vibration damper discussed above, this torsional vibration damper is disadvantageous at lower rates of rotation, but exhibits better dampening of characteristics at higher rates of rotation, for example, above 2,500 RPM, due to the smaller mass moment of inertia.
An object of the present invention is to provide a torsional vibration damper with improved dampening characteristics for introduced torsional vibrations at any desired rate of rotation of the driving means.
The above stated object is obtained by a damper according to the invention wherein the damper has a gearset which is provided with a shift mechanism for separating the driving-side gear set element from the driven-side gearset element.
An advantage of employing a gearset with the damping device of a torsional vibration damper, is that when the elements of the gearset are accelerated, an increased mass moment of inertia occurs which continues to increase with increasing deflection speed between the driving-side transmission element and the driven-side transmission element. The gearset is accordingly maintained in operation as long as a driving device, e.g., an internal combustion engine, connected before the torsional vibration damper, operates at low rates of rotation and therefore in an operating range in which low-frequency torsional vibrations of great magnitude occur which can be adequately damped only with a comparatively large mass moment of inertia. Above a predetermined threshold rate of rotation, for example, 2,500 RPM, at which the damping characteristics of the torsional vibration damper are no longer sufficiently effective due to high-frequency torsional vibrations of smaller magnitude, the shift mechanism is activated so as to effectively disengage the working connection between the driving-side gearset element and the driven-side gearset element, so that the deflection of the transmission elements, relative to one another, no longer results in an acceleration of the gearset elements. Therefore, above this threshold rate of rotation, the torsional vibration damper operates like a torsional vibration damper without a gearset, so that good damping characteristics are also provided above this threshold rate of rotation.
Advantageous embodiments of the invention and shift mechanism can take numerous forms. For example, the shift mechanism, insofar as it acts in dependence on the rate of rotation, can be controlled based on the effective centrifugal force and has, for example, in a simple embodiment, an axial spring which is part of a shift element and which is deformable by the action of centrifugal force in such a way that its axial dimension decreases, but its radial dimension increases. As a result of the deformation of the axial spring, the friction-generating axial force which is exerted by the axial spring on an adjoining part of the shift element decreases, so that this part of the shift element, e.g., a carrier element for receiving the driving-side gearset element, slips relative to the axial spring and accordingly enables the driving-side gearset element to carry out a relative movement which triggers the desired cancellation of the working connection between the driving-side gearset element and the driven-side gearset element.
A shift element of this kind can have a carrier element at which at least one gearset element, for example, the driving-side gearset element, is received. For this purpose, the carrier element, in a simple embodiment, is pressed through proceeding from the opposite side of the gearset to form a bearing pin for the gearset element. This carrier element is preferably movable in the axial direction, but most of all in the rotating direction against the action of the shift mechanism as soon as the axial force exerted by the latter decreases, e.g., when acted upon by a determined centrifugal force. The carrier element is preferably constructed as a ring which is arranged in its radial inner region on a bearing element associated with the hub of the driving-side transmission element. The carrier element is preferably freely rotatable relative to its bearing element, wherein, however, this rotating capability is prevented by the shift mechanism, preferably by means of a frictional engagement, until the predetermined threshold rate of rotation is reached. Above this threshold rate of rotation, however, the carrier element can participate in the movement of the gearset element received by it, as a result of which, the individual gearset elements can no longer move relative to one another and are consequently no longer accelerated relative to one another during relative movements of the transmission elements.
The various features of novelty which characterize the invention are pointed out with particularity in the claims appended to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.